fspilot747
Posts: 3455
Joined: Mon Nov 01, 1999 2:58 am

Quick Question For Cessna 172 Pilots/Students

Mon Feb 10, 2003 4:33 am

I should know this, but I haven't been in this situation in a couple years.

What exactly do you do when your RPM drop exceeds 50 RPM during the run-up magneto check (in regards with cleaning up the spark plugs)? I would ask one of the instructors at the airport, but I'm not gonna be there for a while. I have an idea of what to do, but I want to be certain before I end up in that situation.

Thanks,
FSP
 
flyingbronco05
Posts: 3484
Joined: Fri May 10, 2002 11:43 am

RE: Quick Question For Cessna 172 Pilots/Students

Mon Feb 10, 2003 4:40 am

I was taught to have the engine at 1700 RPM and check the magnetos. They shouldnt go below 1500, i think. It's been a while since I have actually flown in a 172.

FB05
Never Trust Your Fuel Gauge
 
flyingbronco05
Posts: 3484
Joined: Fri May 10, 2002 11:43 am

RE: Quick Question For Cessna 172 Pilots/Students

Mon Feb 10, 2003 4:46 am

b. Magnetos -- CHECK (RPM drop should not exceed 125 RPM on either
magneto or 50 RPM differential between magnetos)

If you get below 50RPM i would NOT take the plane off.

FB05

http://pages.prodigy.net/jedinein/c172sop.html
Never Trust Your Fuel Gauge
 
flyf15
Posts: 6633
Joined: Tue May 18, 1999 11:10 am

RE: Quick Question For Cessna 172 Pilots/Students

Mon Feb 10, 2003 7:09 am

What you're refering to is fouled plugs. I've had it happen to me a few times. The engine will be running fine, upon mag check, when going to left or right the engine will drop oh say, 300rpms, and get pretty rough. To take care of it (burn it off), run the engine up to full power and lean out the mixture and maintain that for a minute or two. Go back and do another mag check. If everything goes as it should, you'll be good to go. If its still running rough (I'm just guessing here, it hasn't ever continued to be rough for me), I suppose you could try to burn it off again, but its most likely something else.
 
sllevin
Posts: 3312
Joined: Wed Jan 30, 2002 1:57 pm

RE: Quick Question For Cessna 172 Pilots/Students

Mon Feb 10, 2003 7:48 am

I agree with with Flyf15, with the exception of running the engine at full power. You'll generate extra propeller wear, and at high power settings running lean can lead to detonation (unless you are SURE you are significantly lean of peak).

At 1700rpm, detonation from running close to peak is very limited, and you aren't spinning the tips nearly as fast near the ground. Expect to run the engine for about 2 minutes to clear the fouling. Beyond that, if it hasn't cleared up, you may have some additional issue.

Steve
 
radarbeam
Posts: 998
Joined: Fri Mar 01, 2002 9:00 am

RE: Quick Question For Cessna 172 Pilots/Students

Mon Feb 10, 2003 8:44 am

The way I do it is

Step on the brakes
Set mags on both
Set power to 2,300 rpm
Lean mixture to lean until rpm drops
leave it about one minute or two
If it's still rough taxi back, shut down and get in another plane

Radarbeam
 
fspilot747
Posts: 3455
Joined: Mon Nov 01, 1999 2:58 am

RE: Quick Question For Cessna 172 Pilots/Students

Mon Feb 10, 2003 9:01 am

So basically, instead of having your mixture full rich, just lean it out as far as you would over 3000 ft? ..or more than that? Then full power? I remember now the full power and mixture lean, just didn't remember how much.

Thanks,
FSP
 
lymanm
Posts: 1100
Joined: Tue Jan 23, 2001 2:30 pm

RE: Quick Question For Cessna 172 Pilots/Students

Mon Feb 10, 2003 10:26 am

Not full power, 2000RPMs. Then lean. It's all in your handy POH!
buhh bye